(va —») (55 des + 5 dt i Men 
— (ga EN dv me v Kad 1 
+ (a 1) (dv, Ou 1 4 I, it dn Oe, din \ + 
Us (ow dv One bia oH) 91)v a0 > he eae 
(va 41) (dv, dy) 1 1 Oe, oy) Lan Fa yy?) | (& ) 7 Ee, (1) 
The quantity (&j), is, see le. p. 104, for normal substances a 
negative quantity. 
If we keep 7 constant for the moment, so if we inquire into 
properties of one of the before-mentioned surfaces, we can derive the 
following rule for the position of the line that connects the two 
coexisting phases. If we for instance imagine on the liquid sheet a 
point determined by vj, zj and y, and if we inquire into the direction 
of the line connecting the coexisting phasis with the chosen liquid 
phasis, so into the quantities proportionate to v,—v,, eye), and 
yay) We bring in point 1 as center a quadric surface: 
aw. , oy oy 
"puedes SEs 
29 be Oz, Ov, vvh-2 u, 1 Ov; "yv +2 
< En ce „ (2) 
We cut that surface through the tangent plane at the liquid sheet, 
then the direction of the line connecting the two nodes, will be con- 
jugate to the section of tangent plane and quadric surface cosines. 
The locus of the middle of the chords, whose cosines are equal to 
A, w and v, is given by: 
and this equation leads to (1), when in equation (1) dT is put 
equal to 0 and when dv, dx and dy, are substituted for v, # and y 
and so when this middle plane is tangent plane to the », 2, y-surface 
under consideration. 
On account of the importance which the surface represented by 
(2) has for the equilibrium of the ternary systems, it deserves a closer 
examination. 
If a definite quantity of a substance, which is ternary composed, 
is to be in equilibrium at given temperature in a given volume 
ow dw LA d d d 
then rep, Pi! nd w— oa iS ~y = must have an invariable value 
